That “hair growth” vitamin could quietly throw off cancer test results—and doctors are raising the alarm. Credit: Shutterstock Hair loss is one of the most upsetting side effects of cancer treatment, and many patients look for ways to bring their hair back. One option that has gained popularity is biotin, a vitamin commonly promoted for stronger hair and nails. But experts say the benefits are uncertain, and the risks may be overlooked. There is little scientific evidence that oral biotin helps